The scope of wireless communications to mobile vehicles is steadily growing to include services that may be requested while the vehicle is off or in a quiescent mode. These services include maintenance and diagnostic functions, system updates, vehicle position determination, unlocking of the doors, or vehicle alarm silencing.
While a number of automobiles have been equipped with analog network access devices, the newest vehicles are more likely to be equipped with CDMA-enabled wireless communication and network-access devices. Code division multiple access, or CDMA, is a digital wireless technology that uses a spread-spectrum technique to scatter a radio signal across a wide range of frequencies and provides a greater total call capacity, improved voice quality and fewer dropped calls in wireless carrier systems.
Normally when the ignition of a network-enabled vehicle has been turned off, it is placed into a discontinuous-receive (DRx) mode, a feature used in cellular-phone radio-based applications to put network access devices and other unnecessary electrical components into a quiescent or sleep mode for as much time as possible. This powered-down state minimizes current drain on the battery. To perform a requested function while the ignition of the vehicle is off, the embedded communication device may be awakened after a predetermined time, the desired function performed, and placed back into the sleep mode. The DRx process may limit the amount of time a network access device or telematics unit can be awake during a wake-up period, and may require quiescent modes of prescribed duration during which the in-vehicle cellular may be unable to register. The time period between wake-up operations may vary from ten minutes to several days or more when a vehicle has not been moved or driven.
Even with newer CDMA-enabled hardware, issues may still arise due to the process in which a phone registers each time a network access device powers up and powers down. If CDMA-enabled network access devices in a large number of vehicles continue to follow registration protocols of wireless network carriers with the prescribed frequency, the CDMA system may be unavailable to service calls. A CDMA cellular phone may normally register one to three times per hour, but when it is incorporated into an in-vehicle wireless communication device with a discontinuous-receive mode, the registration interval may increase, for example, to every ten minutes. Where there is a high concentration of parked vehicles such as an airport, stadium or mall parking lot, CDMA-enabled network access devices may be potentially rendered inoperable by a high volume of the devices cycling through the periodic registration procedures implemented in current wireless carrier systems.
A method is needed to mitigate the risk of excessive registration activity on the network of a wireless carrier while still keeping the CDMA-enabled network access device unit registered in the network system. A desirable method would help maintain the availability of CDMA channels for a vehicle to receive a call page and to perform a service request, while maintaining low power consumption at the vehicle. It is an object of this invention, therefore, to provide a method for registering an in-vehicle communications device in a quiescent vehicle, and to overcome the deficiencies and obstacles described above.